A Java OutputStream wrapping a ByteBuffer

ByteBufferOutputStream.java

/*
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 */

import java.io.OutputStream;
import java.nio.BufferOverflowException;
import java.nio.ByteBuffer;

/**
 * Wraps a {@link ByteBuffer} so it can be used like an {@link OutputStream}. This is similar to a
 * {@link java.io.ByteArrayOutputStream}, just that this uses a {@code ByteBuffer} instead of a
 * {@code byte[]} as internal storage.
 */
public class ByteBufferOutputStream extends OutputStream {

	private ByteBuffer wrappedBuffer;
	private final boolean autoEnlarge;

	public ByteBufferOutputStream(final ByteBuffer wrappedBuffer, final boolean autoEnlarge) {

		this.wrappedBuffer = wrappedBuffer;
		this.autoEnlarge = autoEnlarge;
	}

	public ByteBuffer toByteBuffer() {

		final ByteBuffer byteBuffer = wrappedBuffer.duplicate();
		byteBuffer.flip();
		return byteBuffer.asReadOnlyBuffer();
	}

	/**
	 * Resets the <code>count</code> field of this byte array output stream to zero, so that all
	 * currently accumulated output in the output stream is discarded. The output stream can be used
	 * again, reusing the already allocated buffer space.
	 *
	 * @see java.io.ByteArrayInputStream#count
	 */
	public void reset() {
		wrappedBuffer.rewind();
	}

	/**
	 * Increases the capacity to ensure that it can hold at least the number of elements specified
	 * by the minimum capacity argument.
	 *
	 * @param minCapacity the desired minimum capacity
	 */
	private void growTo(final int minCapacity) {

		// overflow-conscious code
		final int oldCapacity = wrappedBuffer.capacity();
		int newCapacity = oldCapacity << 1;
		if (newCapacity - minCapacity < 0) {
			newCapacity = minCapacity;
		}
		if (newCapacity < 0) {
			if (minCapacity < 0) { // overflow
				throw new OutOfMemoryError();
			}
			newCapacity = Integer.MAX_VALUE;
		}
		final ByteBuffer oldWrappedBuffer = wrappedBuffer;
		// create the new buffer
		if (wrappedBuffer.isDirect()) {
			wrappedBuffer = ByteBuffer.allocateDirect(newCapacity);
		} else {
			wrappedBuffer = ByteBuffer.allocate(newCapacity);
		}
		// copy over the old content into the new buffer
		oldWrappedBuffer.flip();
		wrappedBuffer.put(oldWrappedBuffer);
	}

	@Override
	public void write(final int bty) {

		try {
			wrappedBuffer.put((byte) bty);
		} catch (final BufferOverflowException ex) {
			if (autoEnlarge) {
				final int newBufferSize = wrappedBuffer.capacity() * 2;
				growTo(newBufferSize);
				write(bty);
			} else {
				throw ex;
			}
		}
	}

	@Override
	public void write(final byte[] bytes) {

		int oldPosition = 0;
		try {
			oldPosition = wrappedBuffer.position();
			wrappedBuffer.put(bytes);
		} catch (final BufferOverflowException ex) {
			if (autoEnlarge) {
				final int newBufferSize
						= Math.max(wrappedBuffer.capacity() * 2, oldPosition + bytes.length);
				growTo(newBufferSize);
				write(bytes);
			} else {
				throw ex;
			}
		}
	}

	@Override
	public void write(final byte[] bytes, final int off, final int len) {

		int oldPosition = 0;
		try {
			oldPosition = wrappedBuffer.position();
			wrappedBuffer.put(bytes, off, len);
		} catch (final BufferOverflowException ex) {
			if (autoEnlarge) {
				final int newBufferSize
						= Math.max(wrappedBuffer.capacity() * 2, oldPosition + len);
				growTo(newBufferSize);
				write(bytes, off, len);
			} else {
				throw ex;
			}
		}
	}
}